BRADFORD, Vt. — Bert Dodson, an influential artist and illustrator who spent the bulk of his prolific career in the Upper Valley, has died at the age of 83. A draftsman of daunting skill, Dodson asserted that drawing, and art-making in general, is everyone’s birthright and wrote and illustrated two books on drawing meant to encourage people to take it up regardless of prior experience. “Anyone who can hold a pencil can learn to draw with some degree of proficiency,” he wrote in Keys to Drawing, which came out in 1985. By that time, he was well-ensconced in the Bradford area, having moved there in 1977. He would spend the…